The present disclosure generally relates to methods for humanely stunning and/or slaughtering diaphragm respiratory system animals, such as pigs, sheep, rabbits, cows, and non-diaphragm animals such as poultry (e.g., chicken and quail). More specifically, the present disclosure is directed to a method for slaughtering diaphragm respiratory system animals, such as pigs, using a low atmospheric pressure system with or without the addition of inert gas. In particular, the animals are placed into a chamber, the chamber is sealed, and the pressure in the chamber is reduced along a predetermined pressure curve to a target decompression pressure, and maintained at the decompression pressure for a period of time until the animal achieves a state of death. Also disclosed are methods for humanely slaughtering animals, including poultry or non-poultry animals, using low atmospheric pressure in combination with an inert gas. The methods of the present disclosure are more humane than traditional slaughter techniques, and results in excellent meat quality.
In the meat-processing industry, animals such as pigs and poultry are processed in slaughterhouses into products intended for human consumption. Before the animals can be processed, they must first be stunned and then killed. In order to achieve a humane slaughter, the stunning should be sufficient to render the animal unconscious, so the animal does not experience fear, pain, distress, and/or unnecessary suffering during the slaughter process. The animal should be sufficiently stunned so the animal is immobile, does not regain consciousness during slaughter, and does not struggle to free itself during further processing.
The slaughter of animals such as pigs and poultry has traditionally been achieved, for example, by mechanical stunning (e.g., the captive bolt system), electrical stunning, or gas stunning prior to slaughter. The captive bolt system works on the principle of a gun, by firing a blank cartridge that propels a short metal rod from the barrel. The bolt penetrates the skull bone, causing bruising of the brain, stunning the animal. The position and direction of the shot, appropriate velocity, shape of the bolt, and strength of the cartridge are all critical parameters for a successful stun. Electrical stunning involves exposing the animals to an electric voltage. For example, a low voltage alternating electric current may be applied to the animal by means of two electrodes, which are placed on either side of the brain using tongs. Electrical stunning induces electropletic shock or an epileptic state of the brain. The minimum current, minimum voltage, minimum frequency, frequency of calibration of the equipment, and position and contact location on the animal are all critical parameters to a successful electrical stun. Gas stunning, which is a relatively new technique, typically involves the introduction of gases, such as carbon dioxide plus other inert gases, including argon and nitrogen, into a closed chamber containing the animal.
There are drawbacks associated with each of these known stunning techniques. For instance, it is important that an animal has become insensible after stunning. Poor maintenance of the captive bolt method is a major cause of poor stunning. Both captive bolt and electrical stunning can result in manpower fatigue, which may cause wrongful placement of the devices. Failure of the operator to apply the apparatus to the correct spot may not produce unconsciousness. Similarly, gas stunning requires precise concentration and time to achieve a successful stunning, and does not always achieve sufficient stunning to prevent the animal from regaining consciousness during bleeding. The cost of the gas used in the gas stunning can also add to the overall cost of the slaughter.
Attempts have also been made to stun or slaughter animals using changes in pressure. For example, U.S. Pat. No. 4,829,635 to Tonnies discloses a method for stunning animals, such as pigs, before slaughter using a two-step pressure drop. The animal is enclosed in a chamber that is first evacuated to an intermediate pressure (e.g., 150 mbar) that is well below atmospheric pressure (e.g., 1030 mbar), until the animal loses consciousness but not reflexes. The chamber is then evacuated again to a low pressure (e.g., 30 mbar) well below the intermediate pressure, and the low pressure is maintained until the animal is without reflexes, but heart function remains. Each step is disclosed as taking less than 5 seconds. The chamber is subsequently substantially instantaneously recompressed, causing a supplementary stun effect. One disadvantage to the process disclosed in the Tonnies patent, is that it achieves a stun that results in the continuance of heart function of the animal. If the animal is not immediately slaughtered following stunning, the animal could recover consciousness, which would cause undue stress to the animal. High levels of stress in an animal can reduce the quality of the meat. Additionally, each step in the Tonnies patent is disclosed as taking less than 5 seconds, which is considered to be rapid decompression. Rapid decompression is considered inhumane by groups such as the American Veterinary Medical Association. The Tonnies patent does not provide any details about the chamber used in the stunning.
U.S. Pat. No. 2,588,770 to Sadler discloses an apparatus and method for stunning or killing animals. The process involves a pressure drop, first to a pressure low enough to cause sleepiness or unconsciousness, and then optionally to a lower air pressure which is sufficient to kill. In particular, the apparatus comprises a chamber connected to one or more ballast tank(s), an air pump, and a motor. The air pump is powered by the motor, and draws a vacuum on the ballast tank(s). Upon achieving a vacuum, a valve is opened between the ballast tank(s) and the chamber containing an animal. The opening of the valve causes a sudden equalization of atmospheric pressure in the animal chamber, thus subjecting the animal to low pressure, which causes animal unconsciousness. Suitable pressures for rendering the animal unconscious or for killing the animal are not disclosed. One disadvantage to the stunning method disclosed in the Sadler patent is that the rapid decompression and return to ambient pressure can cause stress to the animal, ear drum damage, and internal organ and tissue damage.
In view of the drawbacks associated with prior stunning and slaughter methods, there is a need for a more humane method of stunning and slaughtering animals, and in particular pigs, that also results in an excellent meat quality.